1. Field of the Invention
The present invention relates to a signal transmission device which performs signal transmission between a plurality of mutually-insulated electric circuits in a non-contact fashion by utilizing a magnetoresistive element.
2. Description of the Related Art
A photocoupler, a pulse transformer and so forth are known as devices for transmitting, in a non-contact fashion, a signal from one electric circuit to another electric circuit in a plurality of electric circuits which are insulated one another. However, a temporal change such as exhaustion and degradation of a light-emitting diode (LED) or decrease in a current-transmission rate, is significant in the photocoupler, and a delay in the signal transmission is large as well. The pulse transformer has a small delay in the signal transmission, although it has several issues in that a shape and weight are large, and an operable temperature is low. There is also known a coupler in which a winding coil of a pulse transformer is replaced by a thin-film coil, although such a coupler is also disadvantageous in that the coil for receiving a magnetic field is inferior in efficiency, and thus power consumption is large.
To address these issues, Published Japanese Translation of PCT Application No. 2003-526083 (JP2003-526083A) discloses a signal transmission device provided with a magnetoresistive element. This signal transmission device detects a change in a current, supplied from one electric circuitry system and flowing in a signal conducting line, in a non-contact fashion with the magnetoresistive element (i.e., the current change is detected in a state in which the signal conducting line is insulated), and transmits the current change to the other electric circuitry system as an electric signal. Such a signal transmission device is drawing attention as having superior operation reliability yet having a simplified structure.